The Biggest Fort in the World

The world’s most formidable fortresses are staggering feats of design, construction and engineering. Even more so when you consider they’re sometimes hundreds of years old. Read on to discover the world’s biggest fort and the location of the oldest fort in the world.

Building Big Engineering
21 February 2023

The rulers are long dead but the world’s most famous forts remain standing, towering over the lands they were built to defend. The contenders for the world’s largest fort are mighty symbols of power and prestige. They litter the globe as staples of world history and narrate tales of glory and misfortune. And when it comes to the biggest forts in the world, they are truly awe-inspiring in their size and grandeur.

In one form or another, defensive walls and fortifications have been necessary for thousands of years. Almost all the world’s major civilisations built citadels, and over the centuries they got bigger, often encompassing entire cities. Rulers needed to protect what they had, to establish administrative centres and demonstrate mighty power. Today, the great fortresses invoke images of fierce battles, rebellions, intrigue and mystery, but what is the world’s biggest fort which still stands today, and where is the oldest existing fort in the world?

For the purposes of this article, we’re not including walled cities such as York in the UK, Dubrovnik in Croatia or Carcassonne in France. We’ll also only consider forts and fortresses that are still standing today.

Qasr Bshir

Roman Fort, Jordan (Photo: Dietmar Rauscher via Getty Images)

Location: Jordan | Built: 4th century AD | Circumference: Approx. 1 acre

While it isn’t the world’s biggest fort, Qasr Bshir in the Jordanian desert is one of the oldest and best preserved Roman forts in the world. Technically a castellum, a small Roman detached fort used either as a signal station or a watch tower, it has never been rebuilt, and is a strong contender for the title of the oldest fort in the world which still stands today. A UNESCO World Heritage Site, Qasr Bshir has been described as ‘a poignant reminder of the long vanquished might of Rome on this, the southeastern fringe of the Empire.’

Cheyenne Mountain Complex

Cheyenne Mountain (Photo: Kevin Moloney via Getty Images)

Location: Colorado, USA | Built: 1967 | Size: Approx. 5 acres

Sitting deep under Cheyenne Mountain in El Paso County in Colorado may not be the biggest fort in the world but it may be the most secure. The Cheyenne Mountain Complex, known as ‘America’s Fortress’, has been home to the North American Aerospace Defense Command (NORAD), US Space Command, Air Force Systems Command, the Air Weather Service, the US Civil Defense Warning Center and FEMA, Federal Emergency Management.

Thanks to twenty-five tonne blast doors, the underground bunker comprising fifteen, three-storey buildings can withstand a 30 megaton nuclear bomb as close as 2,000 metres. The entire complex, built under 600 metres of solid granite, sits on over 1,000 giant springs designed to prevent the facility from moving more than an inch in the event of an earthquake, bomb blast or electromagnetic pulse attack.

Krak des Chevaliers

Krak des Chevaliers (Photo: Vyacheslav Argenberg via Getty Images)

Location: Talkalakh District, Syria | Built: 1031 – 1170 | Size: Approx. 6 acres

Krak des Chevaliers in Syria is one of the world’s great fortresses. Indeed it is probably the most important preserved medieval castle on the planet and a contender for oldest fort in the world. It has been occupied by the Knights Hospitaller, the Mamluk Sultanate and the Ottoman Empire.

Fort Douaumont

Fort Douaumont (Photo: kruwt via Getty Images)

Location: Verdun, France | Built: 1885 – 1913 | Size: Approx. 7.5 acres

Fort Douaumont is one of the most fascinating sites on the famous World War I Verdun battlefield. It was built after the Franco-Prussian War to ensure the area could be defended if an attack should happen in the future. The garrison was built to accommodate over 600 soldiers. However, when it came under attack in the First World War, it was dangerously undermanned and was taken by a German raiding party of less than 100 men. At the end of the war it was largely left to ruin.

Edinburgh Castle

Edinburgh Castle (Photo: John Hamilton via Getty Images)

Location: Edinburgh, Scotland | Built: 11th century | Size: 8.8 acres

Dominating the city skyline, Edinburgh Castle is not only a contender for biggest fort in the world, it’s also one of the most imposing. Britain’s most besieged castle has a long and complex history and over the centuries it has been used as a prison, a royal residence and a medieval citadel.

Tower of London

Tower Of London (Photo: Scott E Barbour via Getty Images)

Location: London, England | Built: 11th – 13th centuries | Size: Approx. 12 acres

Officially called His Majesty’s Royal Palace and Fortress of the Tower of London, one of the city’s most instantly recognisable landmarks is also one of the world’s most famous fortresses. It was founded by William the Conqueror after the Norman Conquest and has been used as a prison, armoury, the Royal Mint, a menagerie and a royal residence. It’s perhaps most famous today as the home of the Crown Jewels.

Windsor Castle

Windsor Castle (Photo: Vladislav Zolotov via Getty Images)

Location: Berkshire, England | Built: 11th century | Size: Approx. 13 acres

One of the world’s most famous forts, Windsor Castle is believed to be the world’s oldest and largest inhabited castle. It was built by William the Conqueror as part of a chain of castles creating a defensive ring around London. Over the thousand years of its life, each monarch has added their own mark to the castle, including Edward IV and Henry VIII.

Fort Jefferson

Fort Jefferson (Photo: Bob Krist via Getty Images)

Location: Florida, USA | Built: 1847 | Size: Approx. 16 acres

Comprising over sixteen million bricks, Fort Jefferson is named after the third US president and is the largest brick-built structure in the USA. It’s also the nation’s third largest fort behind Fort Adams in Rhode Island and Fort Monroe in Virginia and a contender for the world’s largest fort. The original purpose of Fort Jefferson – around 109 kilometres west of Key West – was to deter pirate incursions from the Gulf of Mexico, but it was never finished and never fully armed. It was used only as a prison and a coaling station. It was designed to house 1,000 men and the walls are 2.5 metres thick and almost fourteen metres high.

Prague Castle

Prague Castle (Photo: KavalenkavaVolha via iStock)

Location: Prague, Czech Republic | Built: 9th century | Size: Approx: 17.2 acres

Prague Castle is believed to be the largest ancient fortress in the world. The outer walls measure 570 metres long by around 130 metres wide. The first buildings were constructed in 870. Today, it is the office of the president of the Czech Republic.

Königstein Fortress

Königstein Fortress (Photo: Frank Wagner via Getty Images)

Location: Saxony, Germany | Built: 16th – 17th centuries | Size: Approx. 23 acres

Known as the Saxon Bastille, one of Europe’s largest hilltop fortifications rises 240 metres over the left bank of the River Elbe, one of the longest rivers in Germany. The fortress encloses around fifty buildings, while the ramparts are around 1.8 kilometres long and – in parts – over forty metres high. For centuries it was used as a prison and it’s home to Germany’s oldest preserved barracks and the country’s second-deepest well, at 152.5 metres.

Caerphilly Castle

Caerphilly Castle (Photo: czacio via iStock)

Location: Caerphilly, Wales | Built: 13th century | Size: Approx. 30 acres

Second only in size and scale to Windsor Castle in the whole of Britain, Caerphilly Castle is the largest fort in Wales. It was built by Gilbert de Clare and introduced the idea of concentric castle defences. It is one of the finest remaining examples of medieval castle architecture in the world and one historian said it had ‘the most elaborate water defences in all Britain.’ One of the most famous sights at the castle is the southeast tower in the Inner Ward which, thanks to subsidence, leans outward at an angle of ten degrees!

Citadel of Aleppo

Citadel of Aleppo (Photo: dmitriymoroz via iStock)

Location: Aleppo, Syria | Built: 12th – 13th centuries | Size: Approx. 36 acres

The Citadel of Aleppo is one of the world’s most famous forts and among the oldest forts in the world. The original fortress was believed to have been operational around 3,000 BC, but most of the structure visible today was built by the Ayyubid dynasty in the twelfth century. During its lifespan it has been occupied by, amongst others, the Greeks, Armenians, Byzantines, Ayyubids, Mamluks and Ottomans.

Malbork Castle

Malbork Castle (Photo: DariuszPa via Getty Images)

Location: Malbork, Poland | Built: 1274 – 1406 | Size: Approx. 52 acres

Built by the Teutonic Knights, a German order of religious Catholic crusaders, around 315 kilometres north of Warsaw on the banks of the River Nogat in northern Poland, Malbork Castle is often cited as the biggest fort in the world. It was the largest brick-built castle in the world when it was completed, as well as Europe’s largest fortified Gothic building. Malbork Castle was designated a UNESCO World Heritage Site in 1997.


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